python--if条件判断

if 语句

例子：

people = 20
cats = 30
dogs = 15
if people < cats:
print "Too many cats! The world is doomed!"
if people > cats:
print "Not many cats! The world is saved!"
#if - elif - else
if cars > people:
print "We should take the cars."
elif cars < people:
print "We should not take the cars."
else:
print "We can't decide."

你认为 if 对于它下一行的代码做了什么？ If 语句为代码创建了一个所谓的“分支”，if 语句告诉你的脚本：“如果这个布尔表达式为真，就运行接下来的代码，否则就跳过这一段。”

为什么 if 语句的下一行需要 4 个空格的缩进？行尾的冒号的作用是告诉 Python 接下来你要创建一个新的代码区段。这根你创建函数时的冒号是一个道理。

如果不缩进, 会发生什么事情? 如果你没有缩进，你应该会看到 Python 报错。Python 的规则里，只要一行以“冒号(colon)” : 结尾，它接下来的内容就应该有缩进。

2.应用：

print "You enter a dark room with two doors. Do you go through door #1 or door #2?"
door = raw_input("> ")
if door == "1":
print "There's a giant bear here eating a cheese cake. What do you do?"
print "1. Take the cake."
print "2. Scream at the bear."
bear = raw_input("> ")
if bear == "1":
print "The bear eats your face off. Good job!"
elif bear == "2":
print "The bear eats your legs off. Good job!"
else:
print "Well, doing %s is probably better. Bear runs away." % bear
elif door == "2":
print "You stare into the endless abyss at Cthulhu's retina."
print "1. Blueberries."
print "2. Yellow jacket clothespins."
print "3. Understanding revolvers yelling melodies."
insanity = raw_input("> ")
if insanity == "1" or insanity == "2":
print "Your body survives powered by a mind of jello. Good job!"
else:
print "The insanity rots your eyes into a pool of muck. Good job!"
else:
print "You stumble around and fall on a knife and die. Good job!"

3。if结合raw_input函数使用

next = raw_input("> ")
if "0" in next or "1" in next:
how_much = int(next)